Different Stressors Exposure Differentially Regulate Apelin And APJ Expression In The Rat Hippocampus And Hypothalamus

Backgroud and Objective: Stress refers to systemic nonspecific reaction triggered by various stressors that organisms encounter in life.Moderate stress promote adaptive coping,while chronic or severe stress may result in the disruption of homeostasis and endanger physical and mental health.APJ belongs to G protein-coupled receptors family with seven transmembrane domains.Apelin is the endogenous ligand of APJ.Apelin/APJ system plays pivotal roles in multiple physiological and pathological processes through activation of downsteam signaling pathways.Both hippocampus and hypothalamus are key brain regions participate in regulating stress response.Apelin and APJ are widely distributed in these brain regions.Studies have shown that apelin involved in mediating the neuroendocrine response to stress and exerts cognition improving activities in stressed rats.Meanwhile,Apelin and APJ expression are regulated by stress in some peripheral and central tissues.However,there is few study to investigate the effect of stress on Apelin and APJ expression in the hippocampus or whether different stressors exposure differentially regulate Apelin and APJ expression.Thus,explore the effects of different stressors exposure on Apelin and APJ expression in the rat hippocampus and hypothalamus leads us further understanding the relationship between stress and Apelin/APJ signaling,and provides potential therapeutic target for stress ralated diseases.Methods: In the present study,we set different stress paradigms including forced swimming stress,acute restraint stress,chronic water immersion restraint stress and chronic social defeat stress.Rats were sacrificed 30 min after forced swimming stress and acute restraint stress,or 24 h after chronic water immersion restraint stress and chronic social defeat stress.Hippocampal and hypothalamic tissues were dissected and collected on ice rapidly.The protein expression levels of Apelin and APJ were examined by western blotting assay.Results: Forced swimming stress exposure upregulated both Apelin and APJ expression in the hippocampus.Forced swimming stress exposure did not affect Apelin and APJ expression in the hypothalamus.Acute restraint stress exposure upregulated both Apelin and APJ expression in the hippocampus.Acute restraint stress exposure down-regulated both Apelin and APJ expression in the hypothalamus.Chronic water immersion restraint stress exposure upregulated both Apelin and APJ expression in the hippocampus.Chronic water immersion restraint stress exposure indeed upregulated APJ but did not affect Apelin expression in the hypothalamus.Chronic social defeat stress exposure indeed down-regulated APJ but did not affect Apelin expression in the hippocampus.Chronic social defeat stress exposure down-regulated both Apelin and APJ expression in the hypothalamus.Conclusion: Different stressors exposure differentially regulate Apelin and APJ expression in the rat hippocampus and hypothalamus.